Lightweight composite materials hold promise for the aircraft industry. Fiber composites provide a significant improvement in specific strength and stiffness over conventional metal alloys. Better specific strength and stiffness translates into weight savings, which translates into fuel savings and lower operating costs. Additionally, composites do not corrode like aluminum, and they are more resistant to fatigue.
Composite structures in these aircraft do not readily conduct away the extreme electrical currents and electromagnetic forces generated by lightning strikes.
Aircraft with composite structures may be equipped with protection against electromagnetic effects (EME) from lightning strikes. For example, conductive media may be provided on a surface to divert lightning current away from underlying metal fastener systems. In addition, gaps between fastener parts and gaps between fastener parts and structural members may be filled with dielectric sealant. Even if some current is not diverted, the sealant prevents arcing and sparking across the gaps.
The sealant provides EME protection. However, the process of injecting the sealant is time consuming as it involves multiple steps, including surface cleaning, sealant curing and overfill removal. Moreover, the sealant adds weight to an aircraft. The weight added to a single fastener system might seem insignificant. However, applying the sealant to tens of thousands of fasteners in a single aircraft can add hundreds of pounds.